I'm not denying it. Whm has DD abilities to. As does War. But when they focus on other things. It hurts their dps. Will they be able to do decent damage? yes Will the be able to keep up with pure dd such as war/mnk/drg? No
It's not about what a Job can and can't do. Its about what the jobs main role is in the party and brd's main role is support not dps.